"the Fine Line Between Portrait And Still Life Photography"

hey everyone - i am currently doing my dissertation for a photography degree, and would like if people would give me their opinion on the portrait or still life photography, for example when is a portrait image turned into still life.

in university we were given an assignment to take daylight portraiture photographs using a 5x4 film camera, all of us took the traditional and more conventional route and went straight in and took photographs of people, but one student she took photographs of her belongings - clothes on a line and shoes in a shoe rack - she handed the assignment in and was then told she had to re-take the photographs or she would fail the assignment, it makes me think - when taking photographs of a persons personal belongings is it not also seen as portrait as it represents that person, or is it only a still life photograph? - and what about still life portraiture - can someone explain that, is that a category or is it just a silly made up group for people to insert their work were that do not know were else to put it.

any help wil be truly thankful, - any notes will be taken in - thank you for you help. Jly90 -